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Code Analyzer for C#

There is a newer version: 10.2.0.105762

Why is this an issue?
double.NaN and float.NaN are not equal to anything, not even themselves.
When anything is compared with NaN using one of the comparison operators >,
>=, <, ⇐ or the equality operator
==, the result will always be false. In contrast, when anything is compared with NaN using the inequality operator
!=, the result will always be true.
Instead, the best way to see whether a variable is equal to NaN is to use the float.IsNaN and double.IsNaN methods, which work as expected.
How to fix it
Code examples
Noncompliant code example
var a = double.NaN;

if (a == double.NaN) // Noncompliant: always false
{
  Console.WriteLine("a is not a number");
}
if (a != double.NaN)  // Noncompliant: always true
{
  Console.WriteLine("a is not NaN");
}

Compliant solution
var a = double.NaN;

if (double.IsNaN(a))
{
  Console.WriteLine("a is not a number");
}
if (!double.IsNaN(a))
{
  Console.WriteLine("a is not NaN");
}